The present invention relates in general to filter circuits and, more particularly, to a digital multiband filter.
Digital filters are commonly used in electronic circuit design, for example in television systems, to remove undesired frequencies from incoming video signals. A composite video input signal from a television receiver contains luma (brightness) and chroma (color) information. Before any digital processing an analog-to-digital converter must transform the composite video into digital form. The digital filter then separates the luma data from the chroma data, the latter of which is modulated on a 3.58 MHz sub-carrier. The separation is necessary for applications such picture-in-picture systems where the luma data and chroma data must be separately stored in RAM in order to recall a complete picture to display as a reduced size image superimposed on the larger screen image. Such digital filters with a restricted bandwidth may thus be used to separate and extract the desired luma and chroma data signals from the composite video data signal.
One difficulty with digital filters is that they tend to require large areas when implemented on an integrated circuit. The excessive size requirements in prior art digital filters results primarily from the use of separate filters for processing the luma and for processing the chroma information.
Hence, a need exists to reduce the area requirements of a digital filter.